In an IMS network architecture of the 3GPP, a core network may cover users located in different time zones in a country, for example, the condition in America; therefore, User Equipment (UE), access layer network elements (Access Network Nodes), IMS control layer network elements and service layer network elements probably are distributed in same or different time zones. Information of the time zone in which the UE is located is significant for the operation of operators from perspectives such as charging, statistics and Quality of Service (QoS) control. In current protocol standard of the 3GPP, timestamp related information included in a message of the IMS network architecture is standard time information of Universal Time Coordinated (UTC) format.
From the perspective of charging through which operators can earn a profit, different time zones probably correspond to different configurable rates, or periods with preferential rate probably are set according to time zones; therefore, the information of the time zone in which the UE is located is significant for operators from perspectives such as charging and statistics.
A charging system defined in the current 3GPP includes two parts, namely, offline charging and online charging.
The offline charging is used for reflecting charging and statistics information in near real-time; FIG. 1 shows constitutes of an offline charging function entity in an IMS and the relationship there-between.
Charging Trigger Function (CTF) is embedded in each network element of the 3GPP IMS, including access layer network elements, control layer network elements and service layer network elements, with the main purpose of collecting charging information according to the monitored use of network resources and sending the information to a Charging Data Function (CDF) through an RF interface (Offline Charging Reference Point); the main function of the CDF is to receive an Accounting Request (ACR) sent from the CTF to construct a Charging Data Record (CDR), and to send the CDR to a Charging Gateway Function (CGF) through a Ga interface; the main function of the CGF is to store and manage the CDR received from the CDF and to send the CDR file to a Billing Domain (BD) through a Bi interface.
The online charging is used for performing online credit control and statistics information report of network resources used by the UE in real time. As shown in FIG. 2, an Online Charing System (OCS) is connected with a BD and a Serving Call Session Control Function (SCSCF), and is used for interacting Credit Control Request (CCR) information/Credit Control Acknowledge (CCA) information with an IMS network element through an Ro interface, wherein the IMS network element includes a Multimedia Resource Function Controller (MRFC) and an Application Server (AS).
3GPP TS32.299 defines relevant standards of offline, online Diameter messages ACR/CCR; TS32.298 defines relevant standards of the CDR. The CDR, containing calling and called numbers, service delivery start time stamp, service delivery end time stamp and other fields, is key information for charging calls. A billing System (BS) generally computes fees according to the call time (service delivery time stamp) of a user. The time information is extracted from two Attribute Value Pairs (AVPs) in the ACR, including Session Initiation Protocol Request Timestamp (SIP-Request-Timestamp) and SIP Response Timestamp (SIP-Response-Timestamp). All the information is of Time type, indicating the number of seconds of UTC time format since Jan. 1, 1900.
From the above analysis, it can be known that the information of the time zone in which the UE is located cannot be acquired from current 3GPP standard definitions; such a bill has defects in many aspects such as user charge, bill query, account settlement and account check, for example, when a user is charged in the periods with preferential rate, it is needed to perform preferential computation according to the local time of the user; and errors will occur in the information about user communication time in the statistics information, causing reduction of customer satisfaction and influencing revenue of operators.